Asphalt is a residue which is obtained after most of volatile oils in components of crude oil are evaporated, and has a physical property of being maintained in a liquid or semi-solid state having a high viscosity at a high temperature but being firmly hardened at a temperature less than or equal to room temperature.
Because the asphalt has good plasticity, high water repellency, electrical insulating properties and adhesiveness, and chemically stable characteristics, the asphalt has been widely used for construction materials such as paving materials or waterproof materials. However, the asphalt has drawbacks in that plastic deformation occurs during use when the asphalt is exposed to a high temperature for a prolonged period of time and cracking occurs at a low temperature due to external impacts. In order to solve the above problems, research has been conducted to improve the physical properties of asphalt by adding various polymers.
Specifically, a vinyl aromatic hydrocarbon-conjugated diene block copolymer such as a styrene-butadiene-styrene (SBS) block copolymer has been widely used as a modifier for improving the physical properties of asphalt.
When the vinyl aromatic hydrocarbon-conjugated diene block copolymer is used as the asphalt modifier, much time and cost are required to dissolve the block copolymer at a high temperature. Therefore, the most important physical property of the block copolymer used as the asphalt modifier is compatibility with asphalt.
However, as advancement of oil refining facilities has been continuously made due to an increase in oil prices and energy saving policy, the amount of asphaltene in asphalt, as a refining byproduct, has been increased. Because the asphaltene as an aggregate of aromatic hydrocarbons, includes a large amount of polar functional groups at the ends thereof, the asphaltene has very low compatibility with block copolymers having no hydrophilic functional groups. Thus, a processing time or a manufacturing time of the asphalt may not only be remarkably extended, but a decline in quality of the asphalt, for example, a decrease in elasticity of modified asphalt, may also be caused.
Accordingly, various studies on a method of adjusting a molecular weight of the SBS block copolymer or changing a microstructure of the SBS block copolymer to provide a coupling effect, or a method of adding an additive, such as oil, as a processing aid have been conducted to enhance the compatibility with the asphalt.
By way of example, Korean Patent Publication No. 2016-0052310 discloses that compatibility with the asphalt and physical properties of the asphalt may be improved when a vinyl aromatic hydrocarbon-conjugated diene block copolymer including a predetermined content of a heterologous conjugated diene block having a peak molecular weight Mp is used as an asphalt modifier.
Also, Korean Patent Publication No. 2015-0102869 discloses that modification workability, low-temperature properties and storage stability of the asphalt may be improved when a functionalized vinyl aromatic hydrocarbon-conjugated diene block copolymer in which an aldehyde group is bound to a main chain of a conjugated diene block is used as an asphalt modifier.
Such patents have somewhat improved mixing property with the asphalt, but do not exhibit a sufficient improvement effect. Also, the patents have no ultimate solution because there is a high variation in quality of asphalt and asphalt compositions obtained accordingly also have different modification effects. Thus, there is an urgent need for research on a vinyl aromatic hydrocarbon-conjugated diene block copolymer having excellent compatibility and modifying performance as the asphalt modifier.